Compressor

ABSTRACT

Provided is a compressor for use in a gas well which produces natural gas, wherein the compressor controls the operating state of an impeller to suppress a reduction in the efficiency and the range of operation when liquid contamination occurs. In a compressor used in a natural gas well, contamination of the impeller of the compressor with a liquid component gives rise to a reduction in the compressor efficiency and the range of operation of the compressor. In order to enable a compressor which runs in an operating environment that is contaminated with a liquid component to operate without causing a reduction in the efficiency of the impeller or a reduction in the range of operation, the present invention provides a method of controlling the operating state of the impeller when liquid contamination occurs.

TECHNICAL FIELD

The present invention relates to a compressor and particularly to a compressor that is used in a gas field from which natural gas is produced.

BACKGROUND ART

In recent years, development of conventional gas fields has shifted to development of unconventional gas fields with an increase in demand for fossil fuel and a progress in mining technologies, and it has become necessary to place compressors in severe environments such as in very deep sea or right below gas fields, for example.

In the very deep sea, a method of placing a compressor on a sea bottom at a depth of several hundreds of meters and sending natural gas with a pressure from a reservoir layer in the ground (subsea compressor) has been contrived. Right below a gas field, a method of disposing a compressor inside a gas well at a depth of several thousands of meters in the ground, compressing gas at a bottom portion of the well, and sending the compressed gas out of the ground has been proposed, and compressors for the purpose (downhole compressor) has been studied and developed. A pressure under the ground is high in an initial stage of development, and an inner pressure becomes lower as gas collection advances. Since it is possible to cause natural gas to blow out of the ground when the pressure under the ground of the gas field is high while it is not possible to cause the gas to blow out when the pressure is lowered below a limit, a gas well at a lowered pressure has been regarded as having been exhausted in the related art. However, a considerable amount of natural gas still remains inside the gas field even after the pressure under the ground has been lowered to a level of a pressure that is not sufficient to cause the gas to blow out.

Thus, it is considered to be possible to recover a production ability of the gas field by applying a downhole compressor to boost a pressure right below the gas field.

The subsea compressor or the downhole compressor described above are placed at a bottom portion of a gas field or right below a gas field, an operating environment is significantly severe. Typically, a compressor used in a gas field for producing natural gas is characterized in being placed in an operating environment in which not only natural gas but also a liquid component including water and light liquid-form hydrocarbon called condensate are mixed into a working fluid of the compressor. In particular, the aforementioned environment in the very deep sea or right below a gas field is an environment in which a liquid fraction is significantly high. A liquid component that has entered inside the compressor in such an environment is considered to lead to a reduction in efficiency due to collision against an impeller, a reduction in a range of operation due to blockage of a flow path due to fouling, generation of unstable fluid force, and thinning of the impeller due to erosion, and the compressor used in a gas field for producing natural gas thus requires a technology for running the compressor without degrading performance in an operating environment that is contaminated with the liquid component.

Therefore, the invention relates to a method of controlling liquid droplets mixed into an impeller such that a compressor that runs in an operating environment that is contaminated with a liquid component can run without reducing efficiency and a range of operation of the impeller.

CITATION LIST Patent Literature

PATENT LITERATURE 1: JP-A-2013-508618

SUMMARY OF INVENTION Technical Problem

An object of the invention is to provide a compressor which runs in an operating environment that is contaminated with a liquid component and which is configured to control an operating state of an impeller when liquid component contamination occurs such that the compressor can run without reducing efficiency and a range of operation of the impeller.

Solution to Problem

In order to achieve the aforementioned object, the invention provides a compressor including: a rotation shaft; a motor configured to drive the rotation shaft; an inverter configured to supply electric power to the motor; arithmetic operation means for controlling the inverter; and an impeller attached to the rotation shaft, in which at least information regarding shaft power detected from the motor is used to control a rotating state of the impeller such that adhesion of liquid droplets to blades of the impeller is suppressed.

Further, the arithmetic operation means performs control such that a rotation speed of the motor is temporarily raised via the inverter in a case in which it is determined that a liquid film has been formed, in the compressor according to the invention.

In order to achieve the aforementioned object, the invention provides a compressor including: a rotation shaft; a motor configured to drive the rotation shaft; an inverter configured to supply electric power to the motor; arithmetic operation means for controlling the inverter; an impeller attached to the rotation shaft; and a sensor disposed on an upstream side of the impeller, in which at least information regarding a flowing speed of a liquid from the sensor is used to control a rotating state of the impeller such that adhesion of liquid droplets to blades of the impeller is suppressed.

Further, information regarding liquid droplet diameters is used with at least the information regarding the flowing speed of the liquid from the sensor to control the rotating state of the impeller such that adhesion of the liquid droplets to the blades of the impeller is suppressed, in the compressor according to the invention.

Further, the compressor according to the invention further includes: storage means, in which the storage means includes a database for determining a state in which formation of a liquid film is determined.

Advantageous Effects of Invention

It is possible to suppress a reduction in the efficiency and the range of operation when liquid component contamination occurs. Since no mechanism for removing a liquid component is required, it is possible to reduce the size of equipment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a compressor illustrating a first embodiment of the invention.

FIG. 2 is a sectional view of a compressor illustrating a second embodiment of the invention.

FIG. 3 is a diagram illustrating a relationship between a liquid fraction and shaft power.

FIG. 4 is a sectional view of a compressor in related art.

FIG. 5 is a sectional view of a gas well in which a compressor according to an embodiment of the invention is placed.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the invention will be described in detail based on embodiments illustrated in accompanying drawings.

Embodiment 1

FIG. 5 is a sectional view of a gas well in which a compressor according to an embodiment is placed.

A gas well 100 is a drilled hole that reaches a gas layer 102 from the outside of the ground, and a steel pipe 104 for protecting an inner wall is placed therein. A compressor 1 is attached to an inner wall of the steel pipe 104 at a bottom portion of the gas well 100 with a support member 130. The compressor 1 is connected to a power source device 134 placed above the ground via a power supply cable 132 disposed in the steel pipe 104. A packer (not shown) configured to separate a lower side (upstream side) from an upper side (downstream side) of the compressor 1 and prevent backflow of gas from the downstream side to the upstream side of the compressor 1 is attached to a clearance between the compressor 1 and the inner wall of the steel pipe 104. The compressor 1 suctions natural gas (hereinafter, referred to as atmospheric gas) 120 in the gas layer 102 at a pressure lowered to a level in which the natural gas cannot blow out, compresses the natural gas to a pressure at which the natural gas can blow out, and then discharges the natural gas toward the outside of the ground. The compressed gas 122 discharged from the compressor 1 rises in the steel pipe 104, blows out of the ground, is sent to a separator 140 via a gas transport pipe 142, and is separated into a gas component and an oil component. FIG. 1 is a sectional view of a compressor according to a first embodiment of the invention. As illustrated in FIG. 1, a turbo-type compressor is employed as the compressor 1, the compressor 1 has, inside a casing 11, an impeller 15 that has a rotation shaft 13 configured to be driven and rotated by a motor 12 and blades 14 held by the rotation shaft 13 and provided at substantially equal intervals in a circumferential direction, and includes an inverter 4 configured to convert electric power supplied from a power supply cable 132 and drive the motor 12 and a database 2 as a storage means and an arithmetic operation means 3 that serve as a control mechanism for the inverter 4. In the aforementioned configuration, a speed and a pressure of a working fluid suctioned from a suctioning port due to rotation of the impeller 15 are raised through a rotation action of the impeller 15, and the working fluid is guided to the downstream side.

In a case in which an apparatus in the related art runs in an operating environment that is contaminated with a liquid component, the liquid component mixed into the impeller 15 in the compressor in the related art as illustrated in FIG. 4 adheres to the blades 14 and forms a liquid film. As a result, since shaft power of the impeller 15 increases, this leads not only to a reduction in efficiency of the compressor but also to a stop due to tripping caused by exceeding of allowable shaft power of the motor 12 configured to drive the impeller. Since the liquid film adhering to the blades 14 blocks a flow path, this leads to a reduction in a range of operation and generation of unstable fluid force and also leads to thinning of the impeller due to erosion.

On the other hand, the compressor according to the embodiment is adapted such that in a case in which formation of a liquid film is determined from at least a trend of shaft power acquired from the motor 12 referring to the amount of increase in shaft power with respect to a liquid fraction illustrated in FIG. 3, for example, in the database 2, the arithmetic operation means 3 performs control such that a rotation speed of the motor 12 is temporarily raised via the inverter 4.

Specifically, although only low shaft power is required in accordance with solid line data 302 in an initial stage since there is no adhesion to the blades 14 in a state of the liquid fraction 306, the shaft power increases in accordance with the dashed line 304 if the liquid component mixed into the impeller 15 adheres to the blades 14. The arithmetic operation means 3 determines formation of a liquid film with reference to the amount of increase in shaft power and performs control such that the rotation speed of the motor 12 is temporarily raised.

Since the liquid flowing into the impeller 15 are atomized with shear force due to the rotation speed and are shaped into liquid droplets, and formation of the liquid film is thus prevented as a result, adhesion of the liquid component to the blades 14 is prevented, the amount of increase in shaft power of the impeller 15 is curbed as compared with a case in which the liquid film is formed as illustrated in FIG. 3, and it is thus possible to suppress a reduction in efficiency and a stop due to tripping of the motor 12.

Also, since adhesion of the liquid droplets to the blades 14 is suppressed, it is possible to suppress a reduction in a range of operation and generation of unstable fluid force due to blockage of the flow path. As described above, it is possible to prevent the liquid droplets mixed into the impeller 15 from changing to a liquid film by controlling the rotating state of the impeller 15 using at least the information regarding the shaft power detected from the motor 12 and to operate the compressor 1 without reducing the efficiency and the range of operation of the impeller 15. Note that the invention is not limited to the aforementioned embodiments and various modifications can be made without departing from the gist of the invention.

Embodiment 2

FIG. 2 is a sectional view of a compressor according to a second embodiment of the invention. As illustrated in FIG. 2, a turbo-type compressor is employed as a compressor 1, the compressor 1 has, inside a casing 11, an impeller 15 that has a rotation shaft 13 configured to be driven and rotated by a motor 12 and blades 14 held by the rotation shaft 13 and provided at substantially equal intervals in a circumferential direction, and is provided with a sensor 5, a database 2, arithmetic operation means 3, and an inverter 4 that are disposed on the upstream side of the impeller 15.

In the aforementioned configuration, a speed and a pressure of a working fluid suctioned from a suctioning port due to rotation of the impeller 15 are raised due to a rotating action of the impeller 15, and the working fluid is guided to the downstream side. In a case in which the compressor runs in an operating environment that is contaminated with a liquid component, the liquid component mixed into the impeller 15 in the compressor in the related art as illustrated in FIG. 4 adheres to the blades 14 and form a liquid film. As a result, since shaft power of the impeller 15 increases, this leads not only to a reduction in efficiency of the compressor but also to a stop due to tripping due to exceeding of allowable shaft power of the motor 12. Since the liquid film adhering to the blades 14 blocks a flow path, this leads to a reduction in a range of operation and generation of unstable fluid force and also leads to thinning of the impeller due to erosion.

On the other hand, the compressor according to the embodiment is adapted such that the arithmetic operation means 3 performs control such that a rotation speed of the motor 12 is temporarily raised via the inverter 4 in a case of a state in which formation of a liquid film is determined referring to the database 2 in the storage means based on a threshold value calculated using at least information regarding a flowing speed of the liquid component acquired by the sensor 2 provided on the upstream side of the impeller 15 and further liquid droplet diameters. Since the liquid flowing into the impeller 15 is atomized with shear force due to the rotation speed is shaped into liquid droplets, and formation of the liquid film is thus prevented as a result, adhesion of the liquid component to the blades 14 is prevented, the amount of increase in shaft power of the impeller 15 is curbed as illustrated in FIG. 3, and it is thus possible to suppress a reduction in efficiency and a stop due to tripping of the motor 12.

Also, since adhesion of the liquid droplets to the blades 14 is suppressed, it is possible to suppress a reduction in a range of operation and generation of unstable fluid force due to blockage of the flow path.

As described above, it is possible to prevent the liquid droplets mixed into the impeller 15 from changing to a liquid film by placing the sensor 2 on the upstream side of the impeller 15 and controlling the rotating state of the impeller using at least the information regarding the flowing speed of the liquid component acquired by the sensor 2 and further the information regarding liquid droplet diameters of the liquid and thereby to operate the compressor without reducing efficiency and a range of operation of the impeller 15. Note that the invention is not limited to the aforementioned embodiments and various modifications can be made without departing from the gist of the invention.

REFERENCE SIGNS LIST

1 Compressor

2 Database

3 Arithmetic operation means

4 Inverter

5 Sensor

11 Casing

12 Motor

13 Rotation shaft

14 Blade

15 Impeller 

1. A compressor comprising: a rotation shaft; a motor configured to drive the rotation shaft; an inverter configured to supply electric power to the motor; arithmetic operation means for controlling the inverter; and an impeller attached to the rotation shaft, wherein at least information regarding shaft power detected from the motor is used to control a rotating state of the impeller such that adhesion of liquid droplets to blades of the impeller is suppressed.
 2. The compressor according to claim 1, wherein the arithmetic operation means performs control such that a rotation speed of the motor is temporarily raised via the inverter in a case in which it is determined that a liquid film has been formed.
 3. A compressor comprising: a rotation shaft; a motor configured to drive the rotation shaft; an inverter configured to supply electric power to the motor; arithmetic operation means for controlling the inverter; an impeller attached to the rotation shaft; and a sensor disposed on an upstream side of the impeller, wherein at least information regarding a flowing speed of a liquid from the sensor is used to control a rotating state of the impeller such that adhesion of liquid droplets to blades of the impeller is suppressed.
 4. The compressor according to claim 3, wherein information regarding liquid droplet diameters is used with at least the information regarding the flowing speed of the liquid from the sensor to control the rotating state of the impeller such that adhesion of the liquid droplets to the blades of the impeller is suppressed.
 5. The compressor according to claim 3, further comprising: storage means, wherein the storage means includes a database for determining a state in which formation of a liquid film is determined. 